1. Field of the Invention
The invention relates to an esterification reagent with the anhydride method to determine the hydroxyl number in polyols, and more specially it relates the use of solvents in the absence of pyridine and having improved function.
2. Description of the Related Art
“Plastics-Polyols for use in the production of polyurethane-Determination of hydroxyl number” (ISO 14900:2001(E)) describes the currently accepted acetic or phthalic anhydride methods for hydroxyl content determination of polyethers and polyesters. These methods which use pyridine to dissolve the hydroxy-containing samples is a serious disadvantage. Pyridine is toxic and odorous. It is harmful to your eyes, nose, throat, and skin, and is classified to an acute toxic substance (level 4) in the material hazard classification.
This method is based on the esterification of polymers bearing hydroxyl group(s) by anhydride in pyridine solution according to the following reaction scheme:
A test portion is refluxed in a solution of anhydride in pyridine to esterify the hydroxyl groups present. The reaction is catalyzed by imidazole. The excess anhydride reagent is hydrolyzed with water and the resulting acid is titrated with standardized sodium hydroxide solution. The hydroxyl content is calculated from the difference in titration of the test portion and a blank solution.
Here Pyridine serves as a sample solvent and a proton scavenger (Anal. Chem. 1980, 52, 1374-1376) in order to easily dissolve the sample so that the esterification reaction proceeds more smoothly in a quantitative conversion.
Since pyridine exhibiting a specific and unpleasant odor, analytical operations have been inconvenient. Therefore, solvent candidates that are free from pyridine odors have long been desired.